[CVE-2026-98566][MODERATE 7.0] drm/imagination: clamp freelist reconstruction requests [ Upstream

[CVE-2026-98566][MODERATE 7.0] drm/imagination: clamp freelist reconstruction requests [ Upstream

[AL-KERNEL]

CVE: CVE-2026-98566
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: drm/imagination: clamp freelist reconstruction requests [ Upstream
Commit: b78f8f5532a077baa4aabccf657a4fb3b164659e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b78f8f5532a077baa4aabccf657a4fb3b164659e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98566
Analysis date: Sat, 24 Oct 2026 04:42:35 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
An unchecked firmware reconstruction count causes a concrete variable-length OOB write in a GPU command object that is subsequently submitted, while attacker control of the oversized count remains unproven.

======================================================================
ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-98566 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98566

The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.

The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.

Published priority for this report: MODERATE 7.0
Manual review required: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-98566	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98566 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=2 LEGACY=MODERATE_KPANIC RESULT=SAME V39_AEGIS_ONE_STEP_UP=MODERATE->MODERATE_KPANIC (final reconciliation agrees; DECISION: both MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-787;CWE-125;*CWE-20;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'An oversized firmware freelist reconstruction count can drive reads beyond the fixed request ID array and a copy beyond the fixed response ID array. The response is built in a local command object, so the unchecked copy provides a concrete out of bounds write that may corrupt adjacent command data or stack memory and can at least crash the kernel. For the CVSS the PR:L value reflects a local process with DRM device access that can submit GPU work and potentially reach firmware recovery handling. Direct user control of the firmware supplied count is not demonstrated, so AC:H is used and privilege escalation remains possible but unproven. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 7 and the production ActionableScore returned 4 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage LOW to MODERATE_KPANIC because the ActionableScore threshold rule was applied. KP and FD specialist checks stage MODERATE_KPANIC to MODERATE because KP specialist did not establish a qualifying panic. final reconciliation stage MODERATE to MODERATE_KPANIC because the cross model evidence reconciliation rule was applied. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4 and DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP and V39_AEGIS_ONE_STEP_UP and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 3.0 and ActionableScore 2 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. Cross model aggregation changed the production result under an enabled evidence gated merge rule. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 4)	MAYBE	WARNONLY SIMPLEFIX HARDWARE LINUS  INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4 DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP KPANIC V39_AEGIS_ONE_STEP_UP MANUAL_REVIEW_REQUIRED	-	-	checked

======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=4
ActionableScoreLower=3
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 3.
* Conservative score: 3; no floor or cap applied.
* Raw paranoid score: 4.
* Paranoid score: 4; no floor or cap applied.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

* +2: Concrete variable-length out-of-bounds write. Unbounded `freelist_count` controls `memcpy()` beyond the fixed response ID array in the local command object.
* +1: Plausible kernel crash/strong DoS from corruption of adjacent stack or command-object storage.
* Paranoid +1: The corrupted structured response is subsequently submitted through `pvr_kccb_send_cmd()`. This scores downstream active-state consumption and the credibly firmware-mediated recovery path, not arbitrary-write capability.
* No retry-accumulation point: the patch shows missing bounds enforcement, not a counter accumulating across retries or re-entry. B5-R is therefore not confirmed.
* No Class A: direct attacker influence over `freelist_count`, copied bytes, overwrite extent, or adjacent target is not established.
* No C/I, controlled reclaim, arbitrary write, LPE, or extra availability point is awarded.

3. Reachability analysis

The request originates from GPU firmware. The supplied hints ground only a possible path from a process with DRM device access through submitted GPU work and firmware recovery; they do not prove that this actor can generate an oversized count or materially control the recovery sequence. Render-node or ioctl permissions for the complete trigger are not shown, so both host-admin and below-host-admin reachability remain unresolved. No namespace-scoped capability, UID-0 requirement, special hardware rarity, prior privileged setup, or hard timing race is established.

4. Primitive and severity reading

The exact primitive is an input-count-driven OOB read from `req->freelist_ids`, followed by an OOB write beyond `resp->freelist_ids`. The response belongs to an active structured command and is later consumed by the KCCB submission path rather than merely rejected by a guard.

This is CLASS_B because the memory corruption is concrete but attacker influence and useful overwrite control remain unresolved. It is not a UAF or cleanup-only fault. ImportantCandidate is YES because a variable-size kernel overwrite followed by structured-state consumption needs Important-versus-Moderate review. Auto-downgrade is disallowed because doing so would discard unresolved leverage from a concrete corruption primitive. However, NEW52/B5-R keeping is not independently satisfied: retry accumulation and materially attacker-controlled retries are absent or unproven.

5. One-sentence report phrase

An unchecked firmware reconstruction count causes a concrete variable-length OOB write in a GPU command object that is subsequently submitted, while attacker control of the oversized count remains unproven.

6. Manual review advice

MANUAL CHECK REQUIRED

Confirm firmware-request provenance, DRM-user influence over recovery requests, command-object layout, maximum overwrite extent, and whether corrupted adjacent fields are consumed before validation.

7. Call-site confidence

Call-site confidence: medium

======================================================================
UPSTREAM PATCH SUMMARY
======================================================================

Patch: drm/imagination: clamp freelist reconstruction requests [ Upstream
Commit: b78f8f5532a077baa4aabccf657a4fb3b164659e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b78f8f5532a077baa4aabccf657a4fb3b164659e

Changed files:
  drivers/gpu/drm/imagination/pvr_free_list.c

Diff excerpt:

Not included in this email. See the upstream URL for the full patch.

Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b78f8f5532a077baa4aabccf657a4fb3b164659e

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-98566 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98566

The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.

The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.

The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.

Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:

  Conservative CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7

The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.

CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.

A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.

  Conservative ActionableScore: 3
  Paranoid ActionableScore: 4

The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.

For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:

  ActionableScore below 5   -> MODERATE REGULAR
  ActionableScore 5 or more -> MODERATE 7.0

The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.

There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).

KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.

AL-KERNEL base severity for this report: MODERATE
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): MODERATE 7.0

These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).

Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).